The present invention is directed to a rotational pulse generating circuit for a brush-equipped or commutator DC motor which generates a pulse train signal in synchronization with motor rotation.
The co-pending U.S. Patent Application under the Ser. No. 09/429,922 discloses an electric circuit for detecting a rotational condition of a commutator or brush-equipped DC motor depending on a ripple pulse frequency which is indicative of a rotational number of the commutator DC motor. An output of such a circuit is in the form of a pulse train which is indicative of the rotational number of the commutator DC motor. This circuit is used to control a position of a vehicular movable member such as a seat or window pane which is driven by the commutator DC motor in such a manner that the output pulse train signal is fed to a micro-processor for positioning the vehicular movable member.
On the other hand, using the foregoing positioning device for a long time inevitably causes frictional wear inevitably between a brush and a commutator in the commutator DC motor, which causes the circuit to issue error pulses, thereby raising the question of how to cope with such an issuance of error pulses. The reason is that feeding the error pulses to the micro-processor makes the positioning of the vehicular movable member incorrect to a slight extent which cannot be neglected from the practical view point. Of course, such a problem can be eliminated by periodic inspections. However, doing periodic inspections are very cumbersome.
Thus, a need exits to make the foregoing electric circuit more reliable without periodic inspections.